The invention relates to a device and a method for sensing an object or a person in the interior of a vehicle with a laser outputting laser pulses.
Persons who are displaced far forward in the direction of a dashboardxe2x80x94such as a child in a child seat positioned on a front passenger seatxe2x80x94are subjected to the hazard, that during the operation of a motor vehicle provided with an airbag, of suffering injuries as result of inflation impact of an airbag in the event of an accident. Modern control systems for personal protection aim at switching off the airbag in such situations or inflating it with reduced momentum in order to avoid the risk of injury to a vehicle occupant. In order to determine the position of the vehicle occupant in the vehicle, use is preferably made of contactless, optical sensors.
A known device for the contactless detection of an object or of a person in the interior of a vehicle is known from Published, European Patent Application EP 0 669 227 A1. In the document, the vehicle seat is irradiated by a number of light-emitting diodes. Beams that are reflected from the seat or a person or an object on the vehicle seat are registered by a photodetector field.
The light source used in the optical sensing system is preferably a laser that permits locationally precise scanning by virtue of its monochrome radiation. Laser diodes, and in particular semiconductor laser diodes, are usually used as transmitters. In order to avoid enduring energy loading of persons in the interior of the vehicle by the laser, the laser is pulse-operated. However, even in this. operating mode, the vehicle occupant must not be adversely affected in terms of health by the output laser pulse in any way.
It is accordingly an object of the invention to provide a device and a method for sensing an object or a person in the interior of a vehicle which overcome the above-mentioned disadvantages of the prior art devices and methods of this general type, which allows a laser to be used within a sensing device without adversely affecting the health of an occupant of a motor vehicle.
With the foregoing and other objects in view there is provided, in accordance with the invention, a device for sensing an object in an interior of a vehicle, including: a laser outputting a laser pulse; a sensing device for sensing a characteristic variable of a transmission energy of the laser; and a control device for reducing the transmission energy and for preventing the laser pulse from being emitted in dependence on the characteristic variable sensed by the sensing device.
Here, according to the invention, a characteristic variable which is decisive for the transmission energy of the laser is sensed using a suitable device and, on the basis of an evaluation of this characteristic variable, the transmission energy is subsequently reduced, the following emitted laser pulse having a reduced energy content. Alternatively, the outputting of laser pulses is completely prevented. In order to reduce the energy content of a subsequent laser pulse, its power and/or its pulse length are preferably reduced.
The invention provides the advantage that a vehicle occupant located in the area of radiation of the laser but is at no time subjected to an overdose of laser radiation energy. All the standards relating to the radiation loading of persons when using lasers, for example the IEC standard, are complied with by the invention.
The vehicle occupant is also protected against a malfunction of the control unit that operates the laser: such a control unit is usually embodied as a microprocessor that operates the laser and in doing so determines the pulse width and power of the individual laser pulses. owing to a malfunction of the control unit, it is possible, for example, for the pulse width in the software or the hardware of the control unit to be set to infinite. A permanent laser light is thus emitted. If the laser is connected to an energy source by an electric power output stage which can be controlled by the control unit, the invention also permits for the vehicle occupant still to be protected against excessive radiation loading even if the power output stage is defective and switched to a permanently on state.
The device according to the invention detects such a permanent irradiation from the fact that the sensing device picks up a characteristic variable, such as, in particular, the energy content of a laser pulse, the transmission power or a transmission level, which is decisive for the transmission energy of the laser. The control device subsequently evaluates the picked-up characteristic variable/variables. If an increased energy emission of the laser, and an associated increased irradiation of the vehicle occupant is detected, the transmission energy is reduced or the energy emission of the laser is completely prevented.
The sensing device is preferably configured to sense a characteristic variable of the electrical operating energy of the laser, such as, for example, to sense its operating current, or else to sense a characteristic variable of the optically emitted energy of the laser, preferably using an optical receiver. Because of the proportional relationship between the operating energy of the laser and the energy that is emitted by the laser, both energy variables are a measure of the transmission energy of the laser. This selection possibility when determining the characteristic variables permits a low-cost device to be fabricated, depending on the application.
In advantageous developments of the invention, the characteristic variable is either determined by evaluating a single laser pulse or on the basis of an evaluation of a plurality of laser pulses, in particular within a predefined time period.
Characteristic variables are preferably derived both from the first-mentioned short-term consideration and from the last-mentioned long-term consideration. The control device is then active as an actuator element for reducing or preventing the emission of the transmission energy only if both the long-term characteristic variable and the short-term characteristic variable exceed predefined limiting values and thus a continuously unstable operating mode of the laser or of its drive components is detected.
In one advantageous development of the invention, the hardware of the control device is separated from the hardware of the control unit that controls the laser during normal operation. If a faulty control unit is the cause of a continuous laser pulse, this is detected using the control device that is configured so as to be spatially separate.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is 1illustrated and described herein as embodied in a device and a method for sensing an object or a person in the interior of a vehicle, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.